The present invention relates to metallocarboranes and, in particular to catalytic systems utilizing the metallocarboranes.
In recent years the discovery and utility of homogeneous hydrogenation, isomerization, hydrosilylation and hydrogen-deuterium exchange catalysts have expanded in scope to become one of the largest areas of endeavor in inorganic chemistry. To date, however, there apparently have been no reports of catalytic systems utilizing the very stable family of metallocarboranes and, consequently, there has been no known recognition of what appears to be a high potential value of the metallocarboranes catalysts in the petrochemical industry as well as their general applicability to many homogeneous catalytic transformations.
For reference purposes, the following publications discuss hydrogenation, isomerization, hydrosilylation and hydrogen-deuterium exchange catalysts:
J. Kwiatek in "Transition Metals in Homogeneous Catalysis", G. N. Schrauzer, Ed., Marcel Dekker, New York, N. Y., 1971, pp 13-51. B. R. James, "Homogeneous Hydrogenation," Wiley, New York, N.Y., 1973.
R. Cramer, J. Amer. Chem. Soc., 88, 2272 (1966), and references therein; R. Cramer, Ann. N. Y. Acad. Sci., 172, 507 (1971); B. Hudson, P. C. Taylor, D. E. Webster, and P. B. Well, J. Chem. Soc. A, 37 (1968).
A. J. Chalk, Ann. N. Y. Acad. Sci., 172, 533 (1971).
A. F. Thomas, "Deuterium Labeling in Organic Chemistry," Appleton-Century-Crofts, New York, N. Y., 1971, Chapter 6.
Also, the following references generally discuss metallocarboranes and their stability:
R. N. Grimes, "Carboranes," Academic Press, New York, N. Y., 1970 pp 207-232; M. F. Hawthorne and G. B. Dunks, Science, 178,462 (1972).
The present invention reports the discovery of a family of stable hydridometallic carborane catalysts for use particularly as homogeneous catalysts. The family includes compounds having the empirical formula (PPh.sub.3).sub.2 HMC.sub.2 B.sub.9 H.sub.11 in which M is a metal. Also included are the substituted complexes having the formula R (PPh.sub.3).sub.2 HMC.sub.2 B.sub.9 H.sub.10 in which R is a general designation for substances including CH.sub.3 --, Ph--, CH.sub.3 CH.sub.2 OCH.sub.2 -- and other alkyl and aryl moieties attached to carbon. In particular, the basic unsubstituted compound or complex includes two isomers in both of which the metal molecule represented by M of the empirical may be rhodium or iridium. Also, cobalt and ruthenium complexes having the same stereo chemistry as the rhodium and iridium complexes should demonstrate the same stability and effectiveness.
Analysis of the two isomers shows following formulations in which as already stated, the metal molecule M represents either rhodium or iridium;
I. 2,2-(PPh.sub.3).sub.2 -2-H-2,1,7-MC.sub.2 B.sub.9 H.sub.11 and
II. 3,3-(PPh.sub.3).sub.2 -3-H-3,1,2-MC.sub.2 B.sub.9 H.sub.11.
It is to be noted that these two complexes are numbered I and II and subsequent description will refer to them by these numbers. As will be apparent the rhodium isomers include complexes I and II and the same applies to the iridium isomers. The proposed stereo chemistry for the two isomers is shown in FIGS. 1 and 2 each of which depicts a carborane ligand coordinated to a metal which may be rhodium or iridium. In the ligand, the BH molecules are shown by a clear circle while the CH molecules are a darkened circle. FIG. 1 represents complex I which is a 1,7 isomer, while FIG. 2 represents the II which is a 1,2isomer.
Complexes I and II can be prepared in high yields from the 7,9,-C.sub.2 B.sub.9 H.sub.12 .sup.- and 7,8-C.sub.2 B.sub.9 H.sub.12 .sup.- monoanions respectively, utilizing the scheme diametrically depicted below:
PPh.sub.3 C.sub.2 B.sub.9 H.sub.12.sup.- RhCl.sub.3.3H.sub.2 O .rarw. RhCl(PPh.sub.3).sub.3 EtOH EtOH, .DELTA. NaOAc .dwnarw. MeOH .dwnarw. MeOH .dwnarw. AgBF.sub.4 (yields &lt;90%) HOAc (PPh.sub.3).sub.2 HRhC.sub.2 B.sub.9 H.sub. 11 Rh.sub.2 (OAc).sub.4.MeOH (yields 80-85%).uparw. MeOH .dwnarw. H.sup.+ 60.degree. PPh.sub.3 Rh.sub.2.sup.4.sup.+ .rarw. [Rh.sup.I (PPh.sub. 3).sub.3 ].sup.+ C.sub.2 B.sub.9 H.sub.12.sup.-
As shown in the above diagram, when a methanol solution of the tris(triphenylphosphine)rhodium(I) cation is allowed to react at 60.degree. with a methanolic solution of either (CH.sub.3).sub.3 NH.sup.+[7,9-C.sub.2 B.sub.9 H.sub.12 ].sup.-(Ia) or (CH.sub.3).sub.3 NH.sup.+.sub.-[7,8-C.sub.2 B.sub.9 H.sub.12 ] -- (IIa) high yields (&gt;80%) of yellow crystalline products I and II, respectively, were obtained. Compounds I and II could also be obtained by treatment of [(C.sub.6 H.sub.5).sub.3 P].sub.3 RhCl with a methanolic solution of AgBF.sub.4 and subsequent reaction with Ia or IIa (yields .ltoreq.85%) or by direct reaction of Ia or IIa with [(C.sub.6 H.sub.5).sub.3 P].sub.3 RhCl in alcoholic solutions (yields .ltoreq.90%).
The iridacarboranes, compounds I and II, are prepared using the synthetic routes outlined below:
EtOH IrCl(PPh.sub.3).sub.3 +C.sub.2 B.sub.9 H.sub.12.sup.- .cent. (PPh.sub.3).sub.2 HIrC.sub.2 B.sub.9 H.sub.11 .DELTA. ca 35% .uparw.cyclohexane .uparw..DELTA.H.sub.2 .uparw.ca 65% MeOH (C.sub.8 H.sub.12 IrCl).sub.2 + 4PPh.sub.3 + 2C.sub.2 B.sub.9 H.sub.12.sup .- .cent. red ionic intermediate .dwnarw. AgBF.sub.4 .uparw. C.sub.2 B.sub.9 H.sub.12.sup.- C.sub.8 H.sub.12 Ir.sup.+ + 2PPh.sub. 3 .cent. C.sub.8 H.sub.12 Tr(PPh.sub.3).sub.2.sup.+
It also has been noted that the present metallocarborane catalyst family includes certain substituted complexes. For example, substituted complexes, 1-R-3,3-(PPh.sub.3).sub.2 -3-H-3,1,2-RhC.sub.2 B.sub.9 H.sub.10, where R equals CH.sub.3 --, Ph--, CH.sub.3 CH.sub.2 OCH.sub.2 --, and other alkyl and aryl moieties, have been synthesized in high yields from the reaction of (PPh.sub.3).sub.3 RhCl.sup.2 and the appropriate C-substituted 7-R-7,8-C.sub.2 B.sub.9 H.sub.11.sup.- monoanion.
Both the irida- and rhodacarboranes exhibit extreme stability in the solid state and solutions prepared with CH.sub.2 CL.sub.2, C.sub.6 H.sub.6 and tetrahydrofuran (THF) for use as homogeneous catalysts appear to be indefinitely stable under a hydrogen or nitrogen atmosphere. The rhodacarboranes may be recovered after exposure to a hydrogen atmosphere in hot toluene for 24 to 48 hour periods, while the iridacarboranes appear to be indefinitely stable in solution even under prolonged exposure to the air. The rhodacarboranes slowly decompose over a period of days when exposed to the air.
To postulate the chemical structure of the products, the rhodacarboranes were subjected to a number of tests. From these tests, it was found that the infrared spectra of rhodacarborane compounds I and II contained absorptions characteristic of triphenylphosphine and the carborane moiety, and two additional bands [(2080 and 2120 cm.sup.-)-(2070 and 2110 cm.sup.-.sup.1) Nujol mull]assigned to v(RhH). The first-mentioned band was found for compound II (the 1,2 isomer) and the other bands for compound I (the 1,7 isomer). Elemental analyses, .sup.1 H, .sup.11 B, and .sup.31 P nmr data confirmed the formulation as 2,2-[(C.sub.6 H.sub.5).sub.3 P].sub.2 -2-H-2,1,7-RhC.sub.2 B.sub.9 H.sub.11 (I) and 3,3-[(C.sub.6 H.sub.5).sub.3 P].sub.2 -3-H-3,1,2-RhC.sub.2 B.sub.9 H.sub.11 (II).
The 100-MHz .sup.1 H nmr of II in CD.sub.2 Cl.sub.2 displayed a complex series of resonances centered at .tau.2.73 (30) assigned to the phenyl protons and a broad resonance centered at .tau.7.76(2) assigned to the carboranyl protons. The hydride resonance was observed at .tau.18.4 as a triplet of doublets, upon .sup.31 P decoupling, this pattern collapsed to a doublet (J.sub.P.sub.-H = 29 .+-. 2 Hz, J.sub.Rh -H = 17.+-. 2 Hz). The phenyl resonances of I were centered at .tau.2.75 (30), and the carboranyl resonance was located at .tau.8.74 (2). The high field triplet of doublets was centered at .tau.21.1 and .sup.31 P decoupling collapsed these signals to a doublet (JP-H = 25.+-. 2 Hz, J.sub.Rh -H= 14.+-.2 Hz).
The 101-MHz, proton-decoupled, .sup.31 P spectrum of II in CH.sub.2 Cl.sub.2 displayed a doublet (J.sub.Rh -P=128.+-.20 Hz) centered at -40.8 ppm, while the spectrum of I contained the doublet (J.sub.Rh.sub.-P =144.+-.20 Hz) centered at -41.5 ppm. Although the 80.5-MHz .sup.11 B nmr spectra (in CH.sub.2 Cl.sub.2) of the complexes were broad and unresolved, the proton decoupled spectra were more revealing. The spectrum of II contained resonances at +0.4 (1) +1.2 (1), +8.7 (4) and +20.7 (3) ppm, while I displayed resonances at +1.2 (1), + 7.5 (2), + 12.5 (3), +15.9 (1), and +19.5 (2) ppm. All .sup.11 B chemical shifts reported are from BF.sub.3 . OE.sub.t2. The number in parentheses is the relative area associated with the resonance. The .sup.11 B spectra of both I and II were very similar to the .sup.11 B spectra of 3-(.eta.-C.sub.5 H.sub.5)-3,1,2-CoC.sub.2 B.sub.9 B.sub.11 and and 2-(.eta.-C.sub.5 H.sub.5)-2,1,7-CoC.sub.2 -B.sub.9 H.sub.11, respectively, as reported by M. K. Kaloustian, R. J. Wiersema, and M. F. Hawthorne, J. Amer. Chem. Soc. 94, 6679 (1972).
The complexes are formulated as formal d.sup.6 Rh(III) hydrides with triphenylphosphine ligands occupying two coordination sites. Consistent with d.sup.6 metallocarboranes, it is suggested that the C.sub.2 B.sub.9 H.sub.11.sup.2.sup.- (dicarbollide) ligand is symmetrically bonded to the rhodium atom which completes the carborane icosahedron.
Isomerization Reactions. Benzene solutions (20.degree.-25.degree., under N.sub.2) of I or II (10.sup.-.sup.3 M) rapidly catalyze the isomerization of 1-hexene (0.5 M). Within 24 hr, the reaction mixture contained 1-hexene and cis-2-hexene (total 17%), trans-2-hexene (56%), cis-3-hexene (3%), and trans-3-hexene (24%).sup.3 as determined by glc analysis. The complexes I or II easily could be recovered from the isomerization reactions and the infrared spectra of the recovered compounds were identical to I or II, respectively.
Hydrogenation Reactions. Under a hydrogen atmosphere (1 atm), solutions of I or II (10.sup.-.sup.3 M) in benzene (35.degree.) catalyzed the hydrogenation of 1-hexene (0.1 M). Concurrent isomerization was observed, but at the end of 52 hr, essentially all of the hexenes were converted to n-hexane.
The investigation of the catalytic hydrogenation reaction is summarized in Tables I and II, FIGS. 3 and 4. These tables compare the hydrogenation reactions using various rhoda- and iridacarborane catalysts in two solvent systems (C.sub.6 H.sub.6 and THF, Table I), and compare the activity of the various catalysts (Table II). Comparison of the relative rates of hydrogenation revealed a faster rate in THF, and as the steric bulk of the carboranyl C-substituent increased, the activity of the catalyst increased.
Hydrosilylation Reactions. The rhodacarboranes were found to be efficient catalysts for the hydrosilylation of ketones, and Table III (FIG. 5) lists the data obtained for this system. Two control experiments were performed. In one of these experiments the reaction contained a 0.6M THF solution of substrate ketone under a hydrogen atmosphere, but no catalyst or silane. The second reaction contained substrate and silane under a nitrogen atmosphere, but no catalyst. The reactions were monitored by nmr analysis and no reduction was noted in either case.
Comparison of the data in Table III (FIG. 5) indicates accelerated hydrosilylation in the THF solvent system as compared to benzene solutions. It will be noted that similar behavior also is observed in the hydrogenation reactions already described.
Hydroformylation Reactions. The catalytic application of rhodacarborane I has been extended to the hydroformylation of 1-hexene. A benzene solution of I (10.sup.-.sup.3 M) and 1-hexene (1.0M) was treated with a mixture of hydrogen and carbon monoxide (51.3% H.sub.2) at a combined pressure of 1000 psi. After 18 hr at 45.degree., n-heptaldehyde was isolated from the reaction mixture as its 2,4-dinitrophenylhydrazone derivative. Gas-liquid chromatography verified the presence of n-hexane and established the ratio of n-heptaldehyde: n-hexane as approximately 1:1. A controlled experiment (no catalyst present), which employed identical conditions to that described above, produced no aldehyde or alkane products. Further experimentation has demonstrated that the hydroformylation reaction occurred at 40.degree. under an ambient pressure of water-gas mixture.
Deuterium exchange. As reported in a Journal of the American Chemical Society, 96, 4676 (1974), Elvin L. Hoel, M. Frederick Hawthorne, Compounds 1 and 2 effect deuteration of 1,2-C.sub.2 B.sub.10 H.sub.12 at least one order of magnitude faster than any other presently known catalyst. The following Table provides a comparison of selected catalysts with 1,2-C.sub.2 B.sub.10 H.sub.12 as a substrate:
Table I ______________________________________ Comparison of Selected Catalysts with 1,2-C.sub.2 B.sub.10 H.sub.12 as Substrate Av no. of D in System Catalyst Conditions.sup.a product.sup.b ______________________________________ 1 10% Pd on C (1 g) 3 days, 100.degree. 2 2 (PPh.sub.3).sub.3 RhCl.sup.c 18 hr, 80.degree. 2 3 (PPh.sub.3).sub.3 RuHCl 18 hr, 80.degree. 5 4 (PPh.sub.3).sub.3 RuHCl 3 days, 100.degree. 8 5 I 1 day, 65.degree. 10 6 II 1 day, 65.degree. 10 ______________________________________ .sup.a Except where noted, reactions were with 1 mmol of 1,2-C.sub.2 B.sub.10 H.sub. 12 and 0.05 mmol of catalyst in 20 ml of toluene with D.sub.2 bubbling at .about.3 ml/min. .sup.b Estimated from ir, .sup.11 B nmr, and mass spectra. .sup.c Formed nearly insoluble dimer and slowly decomposed under these conditions.
The results obtained with the catalytic systems described in the above Table I provide an example of the relative activity and selectivity exhibited by these catalysts with a variety of substrates. The tests using present Compounds I and II are included. The order of rates of deuterium incorporation at the four chemically nonequivalent sets of sites in 1,2-C.sub.2 B.sub.10 H.sub.12 was followed by 80.5-MHz .sup.11 B nmr spectroscopy. With increasing deuterium exchange at a site represented by a given resonance, the doublet due to hydrogen coupling collapsed smoothly to a singlet.
The investigations which have been described appear to effectively establish the potential value of metallocarboranes catalysts for effecting isomerization, hydrogenation, hydrosilylation and hydroformulation of various substrates. The carborane cage evidently stabilizes the complexes and allows these species to function in catalytic reactions. With their intrinsic stabilities in the solid state and in solution, coupled with their facile recovery, this class of catalysts should provide very high conversion numbers and reusability. Obviously, they are of high potential value in the petrochemical industry. Also, the preliminary data of the reactions catalyzed by the compounds certainly suggests that they may find general applicability to homogeneous catalytic transformations.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.